Diuresis is an essential part of the management of critically ill pediatric patients. Fluid overload occurs in these patients due to multiple factors. Achievement of appropriate fluid balance is often necessary for clinical improvement. The local standard care for diuresis in the pediatric intensive care unit currently begins with administration of the loop diuretic, furosemide, at a dose of 1 mg/kg every six hours. This medication regimen is adequate for the majority of patients requiring diuresis however some patients develop resistance to its affects over time. At present, there are two alternative stratgies utilized when this situation develops. One treatment is to increase the dosage of furosemide. The other treatment is to continue the same dose of furosemide and add an additional diuretic, chlorothiazide, which acts synergistically with furosemide. The relative efficacy of these two treatment regimens in this population is unkown and both regimens are considered standard care within the pediatric intensive care unit. In our study, we propose to investigate which is the better treatment for achieving diuresis in patients who have experienced inadequate response to initial dosages of furosemide.